If you put it in the skimmer as Tim says, make sure you keep the pump running until it is all dissolved so that you don't have it sitting there in stagnant water getting very acidic. Then when you do turn the pump back on you are sending a big bolus of acidic water thru your pump (think gaskets and such) which isn't so good.
So off the side of the pool (not touching the walls) or in the skimmer.... your call. I prefer to hang it from some pool noodles and let it float around. I can make an "X" out of pool noodles and rubber bands so it won't touch sides of the walls.
I put 3 pounds in skimmer sock, and then put the sock in my pool net at the end of the pool pole. The net on the end of the pole was dangled in the water about two feet in front of a return jet. The other 3 pounds were put in a skimmer sock, and the sock was placed in the bottom of the skimmer. Now, I could have put both bags in either the pool net, or the skimmers. But I was experimenting with which one dissolves faster. The bag in the skimmer dissolved much faster by the way.